Photostabilizers such as hindered amine compounds and ultraviolet absorbers are known to inhibit deterioration of organic materials, such as synthetic resins, caused by light.
Generally, a compound to be used as a photostabilizer is preferably one which has a high melting point and shows limited resin plasticization and evaporation from a resin. However, a photostabilizer having an excessively high molecular weight is restrained from moving in a resin and thus tends to exhibit a reduced stabilization effect.
For instance, hindered amine compounds obtained by reaction between a 2,2,6,6-tetramethylpiperidinol and a fatty acid are capable of imparting excellent weathering resistance despite having a low melting point. They are, however, easily liquefied due to their low molecular weights and, in the production of a masterbatch comprising such a hindered amine compound at a high concentration, there is a problem that the hindered amine compound bleeds out from the surface of the resulting masterbatch, making the surface sticky and causing blocking of the masterbatch.
As methods for improving the above-described problem in the ease of handling of a hindered amine compound-containing masterbatch, for example, there have been proposed a method of replacing a resin additive with one impregnated into a powdery inorganic material having an oil absorption of not less than 150 ml/100 g (Patent Document 1), a method of incorporating a nucleating agent (Patent Document 2), a method of incorporating a benzotriazole-based ultraviolet absorber (Patent Document 3), and a method of separately producing a hindered amine compound masterbatch and a benzoate compound masterbatch and subsequently mixing these masterbatches (Patent Document 4). Further, Patent Document 5 discloses a masterbatch in which a hindered amine compound, a benzoate compound and a benzotriazole-based ultraviolet absorber are incorporated.